Cast "arduino" long via modbus (two 16 bit uints) in int32_t.

Hello,

I am new with linuxcnc and I didn't find an answer to my question. Maybe here is some help.

I build a MPG which is working with an Arduino Nano putting all data via Modbus TCP to LinuxCNC. It works good with mb2hal but i found a problem while setting up the encoder.

When I write the Encoder long from the arudino to modbus the Encoder Signal is cause of ModbusTCP converted to a word (uint16) and mb2hal converts it back to a s32 with the Uint16 variable input.

When I give this Signal to an encoder input it works but when the value jumps from 65535 to 0 and back I have a fast movement on the axis which is jogging. This is not a good solution but I have actually now clue to solve it.

One option would be to cast the variable on the arduino but I didn't find any solution to cast it back in HAL.

Is there any chance to do this or is it posible to change some things on the encoder site to avoid the jump von 65535 to 0 and the movement of my axis?

It would be glad if someone could give me a hint where i should start searching.

If you are sending 32 bits is should be easy to fix but if you are only sending 16 bits
the wrap needs to be handled by the driver or hal code.
This cannot be done with a cast since it requires a simple state machine
(looking at the current and previous count) to detect overflows and
underflows and extend the count range to 32 or 64 bits.
A simple hal component could do this however

I don't unterstand fully. Like I said I am relativly new to this topic. How could I do this in HAL. Didn't find such things in documentation.

In my knowledge Modbus can only send 16 Bit data in a Register. I can put the Value from the Arduino in two registers. But how can I put them together. MB2HAL puts everything in s32 oder float. I have to put 16 bit of the first value and 16 bit of the second value to get a 32 Bit. Is this possible in HAL and if the answer is yes. How can I do this. Are there any examples in the documentation?

Hello JT,

thanks for the information. I think i need a few days to understand that. The documentation looks good. Even vor Noobs like me.I will try to shift it right.

Thank you very much.

Hello

found out that I can use Python for building components as well. This is working fine for my purpose. But I don't find, how S32 in linuxcnc is defiined.

Actually i can't write 0xFFFFFFFF into an s32 input because of overflow. When I print the values in Python I get as output a minus in hex and in bin, which is confusing me a little.

-h7FFFFFFFF or +h7FFFFFFF for -2147483648 to 2147483647

Is there any chance to push a hFFFFFFFF into s32?

I found a solution for my problem.

First long on arduino IDE is no int32_t.
"s32" on linuxcnc uses 2's complement bit and the arduino "long" doesn't.
If u wanna transfer it via modbus u have to split the long in half and shift it together again.
mb2hal writes holding registers (fnct03) always in s32 and float, which r used as input.
After that u have to convert it to get used in HAL.

I am sure it can be done with a c HAL component too.
Take a look here:
linuxcnc.org/docs/2.8/html/hal/halmodule.html
For doing the conversion this helps:
izziswift.com/twos-complement-in-python/